Process for stripping nickel from articles and composition utilized therein

ABSTRACT

The present invention is directed to the chemical removal of adherent nickel deposits on plating racks and the like employing a composition which contains therein nitric acid and sources of chloride, copper and tellurium or selenium ions and to a process for stripping such unwanted deposits from electroplating apparatus without noticeable damage to the base metal and at speeds not normally obtainable with prior art compositions and methods.

United States Patent 1191 1111 3,856,694 Becking Dec. 24, 1974 PROCESS FOR STRIPPING NICKEL FROM 3,365,461 H1968 Saubestre et a]. 134/3 R ICL AND O I O UTILIZED 3,399,143 8/I968 Slominski l34/4l Foelsch 3,709,824 l/l973 Oda etal. [34/41 [75] Inventor: Donald H. Becking, Birmingham, 3,717,520 2/l973 Brindisi v. 156/18 Mich. [73] Assignee: Oxy Metal Finishing Corporation, gzz g sgl g ggg Lovermg warren Mlch' Attorney, Agent, or Firm-B. F. Claeboe [22] Filed: June 18, 1973 [21] App]. No.: 370,889 ABSTRACT The present invention is directed to the chemical re- [52] US Cl 252/101 134/3 134/41 moval of adherent nickel deposits on plating racks and 3 252/79 2 5 the like employing a composition which contains [51] 1111. c1 c23 1/04, 623 l/O8 therein Pi i i9 and Sources of M Copper and 58 Field of Search 252/792, 101, 142; 134/3, L2HEB%2FT"1PH13QE and a Process f P- 134/41; 156/18 pmg suc unwanted deposits from electroplating apparatus without noticeable damage to the base metal and [56] References Cited at) :nodt 111112121233 obtainable w1th pnor art com- UNITED STATES PATENTS p 3,197,341 7/1965 Wallace 134 3 3 Clam, N0 Drawings PROCESS FOR STRIPPING NICKEL FROM ARTICLES AND COMPOSITION UTILIZED TI-IEREIN BACKGROUND OF THE INVENTION It is known in the art to which this invention pertains that nickel and related metallic coatings on the contact tips of the plating racks of electroplating apparatus can be remove by either mechanical means or chemical techniques. In the mechnical approach it has been conventional to use a hammer or like too] means to shatter the unwanted nickel deposit on the contact tips, and while this treatment is generally effective, it suffers from the disadvantages of being time-consuming and may ultimately result in damage to the metal base. Then too, some plating racks contain several hundred individual tips, so that mechanical removal of the unwanted coatings thereon leads to substantial labor costs.

Chemical methods for dissolution of the nickel deposits on stainless steel racks have generally employed nitr c acTl, and MEETS approach represents an improvement over the hammer method, the use of nitric acid by itself is tedious since nickel is only slowly attacked by this acid. It has accordingly been customary to add a catalyst such as a chloride ion, but this substance in the presence of strong nitric acid forms nitrosyl chloride which is a gas at temperatures above about- 5.5C., and accordingly. its benefit to the stripping solution is soon lost by volatilization. The addition of other ions to the solution has also been proposed, as the i g da t e ion disclosed in Pat. No. 3,399,143; however, following these teachings does not obviate the objection of relatively slow stripping speeds, and may under particular conditions cause damage to the stainless steel contact tips.

SUMMARY OF THE INVENTION The instant invention is particularly directed to a novel composition for removing nickel and generally similar unwanted deposits from plating racks and like articles and to a process for utilizing said composition. the formulation conceived by applicant comprising about 4.5 to 14.5 moles/liter of 4 .Z Be r1 it r i g a gi d a chloride ion in the an idu nt of 0.0] to 0.5 moles/liter, a copper ion in the amount of about 0.01 to 0.l moles/- liter, and a source of tellurium or selenium ions in the amount of approximately 0.005 to 0.2 moles/liter. Preferably, the molar ratio of tellurium or selenium ions to chloride ions is in the general range of about one to three.

While applicant does not wish to be bound by a particular theory. it would appear from work performed to date that tellurium or selenium when admixed with the other constituents of the solution herein disclosed in the general molar ratios above set forth possesses filmforming capabilities. This is perceptible to the naked eye when an examination is made of a stainless steel substrate, and is the apparent reason why there is no noticeable attack upon the surface being stripped and also why unwanted nigkel deposits can be removed at si kjepr xim lebi lfaste nthan emmefiie l available plating solutions.

DESCRIPTION OF THE PREFERRED EMBODIMENT The stripping solution employed in the practice of this invention may be prepared by either one of two procedures. First, there can be initially formed a sodium or potassium salt of tellurium dioxide (tellurous acid anhydride) or selenium dioxide (selenous acid anhydride) by mixing approximately l5 grams of Te 0 or Se 0 with about 10 to 12 ml. of NaOH or KOH, diluting the solution obtained to about 150 ml., and thereafter filtering out the precipitate. A preferred concentration for the hydroxide used is about 50%. The sodium or potassium tellurite or selenite obtained is then combined with measured quantities of nitric acid, cupric sulfate and sodium chloride to provide the novel stripping solution of this invention.

A second procedure for formulating the stripping solution is to directly admix predetermined amounts of Te 0 or 5e0 HNO CuSO, 5H O, and NaCl. This procedure Ts somewhat less expensive than going through the first approach, however, at times it may be found that combining the TeO or SeO directly with HNO produces a somewhat violent reaction. The first mentioned procedure is accordingly preferred at the present time.

The invention will now be more fully described with reference to the following examples, which were run at a solution temperature of approximately 40C.

EXAMPLE I A solution was made up of 500 mil. HNO 5.7 g. Cu- SO .5H O, 3.3 g. NaCl and 3.0 g. FeCl which were diluted to l liter. A stainless steel part having a nickel deposit thereon of about 1 mil in thickness was immersed therein. and it took about 87 seconds before the deposit was removed.

EXAMPLE II There was formulated a solution containing 500 ml. HNO 5.7 g. CuSO .5H O, 3.3 g. NaCl, 2.0 g. ofa commercially available strip aid (composition unknown), and this mixture diluted to 1 liter. It took about 141 seconds to remove a 1 mil thick nickel deposit from a stainless steel part.

EXAMPLE III A solution was made up of 500 ml. HNO 5.7 g. Cu- SO .5H O, 3.3 g. NaCl and 1.5 g. Na TeO which were diluted to 1 liter. It only took 38 seconds to strip a l mil nickel deposit from a stainless steel part.

EXAMPLE IV The procedure of Example III was followed except that Na SeO was substituted for the Na TeO The same thickness deposit was removed in 35 seconds.

' EXAMPLE V The procedure of Example III was again followed, except that 1.5 g. NaF was used in place of the Na TeO A nickel deposit of the same thickness took l 10 sec onds to be removed from a stainless steel part.

EXAMPLE VI There was formulated a stripping solution containing 500 ml. HNO 5.7 g. CuSO .5H O, 3.3 g. NaCl, 1 g. KBrO and 0.3 g. KIO which was diluted to l liter. A l mil nickel deposit was removed from a stainless steel part in seconds.

EXAMPLE Vll A solution was made up of 500 ml. HNO 5.7 g Cu- SO .5H O, 3.3 g. NaCl and 1 ml. bromine, the mixture being diluted to 1 liter. A 1 mil nickel deposit was stripped from a stainless steel part in 94 seconds.

EXAMPLE Vlll There was formulated a stripping solution containing 500 ml. HNO 5.7 g. CuSO .5H O, 3.3 g. NaCl. and ml. Na TeO solution prepared as earlier described, and this mixture was diluted to 1 liter. A nickel deposit of a thickness of 1 mil was stripped in only 58 seconds.

EXAMPLE lX A solution was prepared as in Example Vlll, but the amount of NaJeO solution was increased to ml. A deposit of the same thickness was removed in only 33 seconds.

EXAMPLE X There was formulated a stripping solution containing 2 g/l TeO 600 g/l HNO 5.7 g/l CuSO .5H O and 3.3 g/l NaCl. An unwanted nickel deposit one mil thick was stripped from a stainless steel part in 27 seconds. which is about 30% faster than commerically available strippers.

In the exemplary formulations set forth above, potassium hydroxide can readily be substituted for sodium hydroxide; potassium, manganese or cupric chloride can be used in place of sodium chloride; and cupric nitrate or chloride are substituents for cupric sulfate. Further, if desired. a portion of the nitric acid may be replaced by an equivalent (i.e., acid equivalent) amount of sulfurric acid, thereby satisfying the hydrogen ion requirement by a less expensive acid.

Various modifications in the compositions of this invention have been pointed out herein. and these and other changes can of course be effected without departing from the spirit of the invention of the scope of the subjoined claims.

I claim:

1. A composition for stripping accumulated nickel deposits from plating apparatus and the like, which comprises nitric acid and sources of chloride, copper and tellurium or selenium ions, said chloride ion being present in concentrations of about 0.01 to 0.5 M and said tellurium or selenium ions being present in small but effective amounts sufficient to accelerate the stripping rate without noticeable deleterious effects upon the plating apparatus.

2. A composition as defined in claim 1, in which the tellurium or selenium ions are present in concentrations of about 0.005 to 0.2 M.

3. A composition as defined in claim 1, in which the copper ion is present in concentrations of about 0.0l to 0.5 M.

4. A composition as defined in claim I, in which the nitric acid is approximately 42 Be. and is present in an amount of about 4.5 to 14.5 M.

5. An aqueous solution for stripping accumulated nickel deposits from plating apparatus, which contains therein about 2 to l0 grams per liter of tellurium or selenium dioxide, 600 to 850 grams per liter of nitric acid, 2 to 20 grams per liter of copper sulfate, and 3.5 to 35.5 grams per liter of a source of chloride ions.

6. An aqueous solution as defined in claim 1, in which the source of chloride ions is selected from the group consisting of sodium chloride, potassium chloride, manganese chloride and cupric chloride.

7. In a method of stripping nickel deposits from articles by immersing them in a concentrated nitric acid solution containing a chloride catalyst. the improvement which comprises adding to said solution a small but effective amount of a selenite or tellurite compound capable of providing selenium or tellurium ions in the solution.

8. A stripping method as defined in claim 7, in which the selenium or tellurium ions are present in concentrations of about 0.005 to 0.2 M. 

1. A COMPOSITION FOR STRIPPING ACCUMULATED NICKEL DEPOSITS FROM PLATING APPARATUS AND THE LIKE, WHICH COMPRISES NITRIC ACID AND SOURCES OF CHLORIDE, COPPER AND TELLURIUM OR SELENIUM IONS, SAID CHLORIDE ON BEING PRESENT IN CONCENTRATIONS OF ABOUT 0.01 TO 0.5 M AND SAID TELLURIUM OR SELENIUM IONS BEING PRESENT IN SMALL BUT EFFECTIVE AMOUNTS SUFFICIENT TO ACCELERATE THE STRIPPING RATE WITHOUT NOTICEABLE DELETERIOUS EFFECTS UPON THE PLATING APPARATUS.
 2. A composition as defined in claim 1, in which the tellurium or selenium ions are present in concentrations of about 0.005 to 0.2 M.
 3. A composition as defined in claim 1, in which the copper ion is present in concentrations of about 0.01 to 0.5 M.
 4. A composition as defined in claim 1, in which the nitric acid is approximately 42 Be. and is present in an amount of about 4.5 to 14.5 M.
 5. AN AQUEOUS SOLUTION FOR STRIPPING ACCUMULATED NICKEL DEPOSITS FROM PLATING APPARATUS, WHICH CONTAINS THEREIN ABOUT 2 TO 10 GRAMS PER LITER OF TELLURIUM OR SELENIUM DIOXIDE, 600 TO 850 GRAMS PER LITER OF NITRIC ACID, 2 TO 20 GRAMS PER LITER OF COPPER SULFATE, AND 3.5 TO 35.5 GRAMS PER LITER OF A SOURCE OF CHLORIDE IONS.
 6. An aqueous solution as defined in claim 1, in which the source of chloride ions is selected from the group consisting of sodium chloride, potassium chloride, manganese chloride and cupric chloride.
 7. IB A METHOD OF STRIPPING NICKEL DEPOSITS FROM ARTICLES BY IMMERSING THEM IN A CONCENTRATED NITRIC ACID SOLUTION CONTAINING A CHLORIDE CATALYST, THE IMPROVEMENT WHICH COMPRISES ADDING TO SAID SOLUTION A SMALL BUT EFFECTIVE AMOUNT OF A SELENITE OR TELLURITE COMPOUND CAPABLE OF PROVIDING SELENIUM OR TELLURIUM IONS IN THE SOLUTION.
 8. A stripping method as defined in claim 7, in which the selenium or tellurium ions are present in concentrations of about 0.005 to 0.2 M. 